The Investigation Of Laser-induced Plasma With Metal Targets Under Atmosphere Condition

Laser-induced breakdown spectroscopy (LIBS) is a fast and useful qualitative andsemi-quantitative technique for the determination of elemental composition of a widerange of materials, under various analytical conditions. Analysis techniques based onspectra have the advantage of simultaneous multi-element detection, rapid analysis,non-destructive. While qualitative technique is based on the LTE condition of plasma, thetwo significant parameters of plasma are electron density and temperature, it is necessaryto measure these two parameters. Therefore the determination of electron density andanalysis its influential factors are our main purpose, it can provide guarantee forquantitative technique.The thesis begins with a brief background introduction of this work. After that is thedescription of fundamental mechanical of LIBS, spectral broadening mechanical, thetheory of measurement of plasma parameters, a detailed review of the status quo and thetendency of this technique. The bulk of author’s contribution, within the general groupeffort,was described in Chapter4and Chapter5.In this paper, using1064nm Q-Switch laser beam as the source, it was used togenerate aluminum, nickel and copper plasmas in the air. The environment backgroundeffect deeply influences the physical characterization of plasma. The single pulse energywas10mJ,15mJ,20mJ respectively. There atomic lines Al I308.20nm, Cu I324.75nmand H line were chosen for investigation. For these three lines, we obtained theevolution trend of the spectral broadening at different time delay. The results indicate thatthe spectral broadening of Al I308.20nm and Cu I324.75nm at the laser energy of20mJwere less than the spectral broadening at the laser energy of10mJ and15mJ.For Ha line,we obtained the opposite results. The spectral broadening of H line at the laser energy of10mJ was less than the spectral broadening at the laser energy of20mJ and15mJ. Theplasma temperature was higher at the laser energy of10mJ than the plasma temperature atthe laser energy of20mJ and15mJ.It was also found that the air background have a bigeffect on the physical characterization by laser induced plasma, most of the laser energywere absorbed by the air especially at the laser energy of20mJ, only few laser energywere absorbed by the sample, but at the laser energy of10mJ, there are a lot of laserenergy were absorbed by the sample, the plasma shielding effect fade away. For thecalculation of electron density, we found the same phenomenon. After the above work, we proceed the other work, that is LIBS instrumentalbroadening and its effect on the measurement of electron density by laser-induced plasma.There are many influential factors for instrumental broadening, the instrumentalbroadening is very important, but we often ignore it. In reality, spectrometers are not idealand a source emits radiation which can’t consist of a single monochromatic wavelength,so they produce an apparent spectral broadening of the purely monochromatic wavelength.It is necessary to assess how instrumental broadening effect on electron density. In thispresent paper, we use HG-1standard mercury and argon light source to measureinstrumental broadening, although the instrumental broadening are usually in the order ofmagnitude0.1nm, the instrumental broadening numerical range from0.08nm-0.19nm, therelationship between the line profile and instrumental broadening profile is convolution.We found that if the observed experimental profile are equal to instrumental broadening,the instrumental broadening could make large contribution to the observed experimentalprofile, so when we adopt plasma emission line to calculate electron density,we shouldconsider instrumental broadening effect. In general, if the broadening of emission line isfour times or even bigger of instrumental broadening, the relative error is less than10%,the influence of instrumental broadening can be neglected for these specific of observedexperimental profile, especially for H line which has large spectral broadening. For thecalculation of electron density, we also have the same conclusion.In the last part of this thesis, a general discussion of the work and some suggests ofpossible future developments have been given in chapter6.